A TE to TM optical mode converter transforms the TE mode to the TM mode in a waveguide and vice versa. Such converters are used to fabricate a variety of integrated optical devices, such as wavelength filters and polarization transformers. Wavelength filters are important components for multiplexing/demultiplexing applications in lightwave systems. Polarization transformers, on the other hand, compensate for undesirable polarization changes in a transmitted optical signal with time and distance and are necessary for a class of interferometric signal processing techniques. Heterodyne detectors and fiber interferometers utilize such techniques and, therefore, require an optical signal polarized along a specified direction.
In one type of optical mode converter, an optical waveguide comprising a birefringent material is subjected to a predetermined electric field to attain TE to TM mode conversion. Although the mode conversion provided by this device is highly wavelength selective, it is also known that the wavelength of the mode converted can be tuned by the use of a second electric field applied to the optical waveguide. See, for example, U.S. Pat. No. 4,273,411 to applicant, dated June 16, 1981. While the use of a second electric field provides a considerable tuning range, the voltages required to establish the necessary electric fields for mode conversion and tuning are greater than is desirable for particular lightwave applications.